This article will detail how to enable tipping at the point of sale.
First, from the POS, click the gear icon in the top right, then payment configuration.
In this screen, put a check in the box to the left of the word TIP, and click Save.
Now, when you are tendering a sale, there will be a button marked TIP on the payment screen. A tip can be accepted like any other form of payment.
Tips will show up like any other payments in the back office, on the Sales/Payments screen. Note that the type of payment will indicate that it is a tip.